Usually a cancelled application means you entered some sort of information incorrectly. Most commonly, it is your name, forgetting a middle name, wrong county for county of your documents, or not being in the country where you applied
Yes, this has happened multiple times - I believe from Japan, Dubai and several others. If they determine that you don’t need a DTV, but need a short term visa, they will give you the METV. Most commonly it happens when people sign up for courses that are too short (less than 6 months). What embassy did you apply through and if soft power, how long was the course?
What are you specifically asking help for? They have four request. First, they want you to draft a letter stating your career path, how you got to where you are and where you want to go professionally. Then they want you to make copies of each page of your passport with today’s date in the image, to prove that you are still in your the geographic location (no exit stamps, etc). Want proof of the funds in a personal savings account and then want proof that you make money from your digital nomad job (payslips line up with deposits, tax forms, etc).
I don’t see any fear mongering. Mostly people telling their experiences. I have entered 10-15+ times on my DTV. First time I had issue was last week, but I am confident it had to do with coming from Cambodia and nothing to do with the DTV.